Some implantable medical devices such as pacemakers can be used to treat patients suffering from various heart conditions that can result in a reduced ability of the heart to deliver sufficient amounts of blood to a patient's body. In some cases, heart conditions may lead to rapid, irregular, and/or inefficient heart contractions. To help alleviate some of these conditions, various devices (e.g., pacemakers, defibrillators, etc.) can be implanted in a patient's body. Such devices are often used to monitor heart activity and provide electrical stimulation to the heart to help the heart operate in a more normal, efficient and/or safe manner.
Prior pacemakers have generally used one or more transvenous leads with intracardiac electrodes to deliver pacing therapy. Newer generation devices may take the form of a leadless cardiac pacemaker (LCP), such as the Medtronic Micra™ or Nanostim™ leadless pacemakers, as well as other LCP products that are in development.
The pacing pulse delivered by a pacemaker is intended to evoke a response by the myocardium. When the pacing pulse causes the desired evoked response (typically an effective and appropriately times contraction of one or more chambers), the pacing pulse is said to have “captured” the relevant chamber. For purposes herein, the evoked response to a pace pulse that captures the relevant chamber is termed an “evoked capture response.” Typically effective capture requires at least a threshold voltage or current be output; this capture threshold can vary in a given patient for various reasons. Setting the output energy of a pacemaker too low can fail to ensure reliable capture; setting the output energy too high can waste current and reduce battery life of the typically non-rechargeable battery. As a result, periodic or occasional confirmation and/or adjustment of the output energy of a pacemaker may be performed to ensure reliable capture without wasting energy. Such adjustment requires the ability to verify pacing capture. Some devices may be setup to verify pacing capture on an ongoing bases, rather than as a part of a test procedure. New and alternative methods for pacing capture verification are desired.